Of Gravity and Its Order: Levers and the Balance
The center of rotation dividing lever from counter-lever, and right-angled pendants
Under 'Of gravity and its order', Leonardo lays out a program for treating weights: first describe the real powers, then the semi-real, then the potential 'virtue'. He defines the center of rotation as that which divides the power of the lever from the power of its counter-lever, whose motions are always contrary about that center, and states that every power joined to a lever meets it at a right angle with one side rising from the center of rotation. Real arms contain their potential arms only when in the position of equality, and the pendant's junction with the balance arm is always its nearest part. Marginal figures show a horizontal beam tied to a pulley, loaded with weights.
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The center of rotation divides lever from counter-lever
The center of rotation is that which divides the power of the lever from the power of its counter-lever, and the motions of lever and counter-lever are always contrary in their revolution about that center. All powers joined to the lever meet it at a right angle whose one side springs from the center of rotation.
Real arms contain potential arms only in the position of equality
The real arms of the balance never contain the potential arms within themselves unless they stand in the position of equality, and the junction of the real or potential pendant with the balance arm is always the pendant's nearest part. The first straightness the pendant acquires after that junction shows the straightness of the potential pendant meeting the potential lever at a right angle.
